The present invention resides generally in the field of chlorinated pyridines. More particularly, the present invention relates in one preferred aspect to processes for preparing 3,5-dichloropyridine by dechlorinating 2,3,5,6-tetrachloropyridine in an acidic medium such as that provided by an alkanoic acid, especially acetic acid.
As further background, polychlorinated pyridine derivatives are important intermediates in the preparation of pesticides. Consequently, much effort has been made at both the academic and industrial levels to find improved, economically-practicable processes for their preparation.
3,5-Dichloropyridine is one such intermediate. Proposed processes for its production have been widely diverse and have included both the selective chlorination of intermediate compounds, the selective dechlorination of higher-chlorinated pyridines, and other routes.
For example, JP011211268 (1989) describes the preparation of 3,5-dichloropyridine by dechlorinating chloropyridine compounds under catalytic hydrogenation conditions in the presence of palladium on carbon. JP 03200769 (1991) describes a process for oxidizing hydrazinopyridine derivatives to give chloropyridine compounds.
Despite work toward convenient and effective routes to 3,5-dichloropyridine, there remain needs for improved processes for the practicable, commercial-scale production this compound. The present invention is addressed to these needs.